The death toll in coordinated ISIS suicide bombings and shootings in southwestern Syria rose to nearly 250 overnight, more than half of them civilians, the Syrian Observatory for Human Rights said Thursday.
Wednesday's attacks hit Sweida, a Druze-majority province mostly held by the regime which had remained relatively insulated from the country's seven-year civil war.
The death toll climbed steadily throughout the day and into the night, the Britain-based monitoring group, said.
"The toll is now 246 people dead, including 135 civilians," said Observatory chief Rami Abdel Rahman.
The others killed were pro-regime fighters or residents who had taken up arms to defend their villages.
"The toll keeps rising as civilians who were wounded are dying and people who were unaccounted for are found dead," Abdel Rahman told AFP.
The onslaught began with a triple suicide bombing in the city of Sweida, which was followed by attacks with guns and explosives on villages to its north and east.
A fourth blast hit the provincial capital later in the day.
ISIS claimed the assault hours later. At least 45 militants died carrying it out, the Observatory said.
It added that it was the worst bloodshed to hit Sweida province since the civil war began in 2011.